The Effect of Soil The Effect of Soil HydraulicHydraulic Properties Properties

and Deep Seepage and Deep Seepage Losses on Drainage Losses on Drainage

Flow using Flow using DRAINMODDRAINMOD

The Effect of Soil The Effect of Soil HydraulicHydraulic Properties Properties

and Deep Seepage and Deep Seepage Losses on Drainage Losses on Drainage

Flow using Flow using DRAINMODDRAINMOD

Debjani DebDebjani Deb2626thth April, 2004 April, 2004

Introduction

• Drainage is the practice of removing excess water from the land and is used as one of the most important land management tools for improved crop production.

• The portion of rainfall or applied irrigation water that in excess of the water holding capacity passes through the rooting zone and is subsequently unavailable for crop use is known as Deep Seepage.

• Deep seepage contributes a portion of base flow in the stream flow.

Background A hydrological assessment using DRAINMOD has already been done

on the Animal Science Watershed based on the following assumption:

The impermeable layer of the watershed was at 6 ft deep with no Deep Seepage

The estimation of Soil Types was based on visual assessment from the USDA soil map.

Based on the assumptions the previous study had the following limitation:

Since Deep Seepage losses contribute to the base flow and Deep Seepage losses were not taken into consideration, the analysis of the Base Flow in the previous study is not precise.

Estimation of Soil Types were not accurate and hence introduced errors in the analysis

Objective

•Assess the error encountered in drainage

flow due to uncertainty in soil hydraulic properties and deep seepage losses

Model Description

• DRAINMOD is a computer simulation model, designed for soils with high water table and subsurface drains.

• Simulates the hydrology of a poorly drained soil and models the field scale effects of drainage on related water management systems.

Governing Water Balance Equations……

• The water balance for a time increment ∆t can be written as,

•∆Va = D + ET + DS – F• The amount of run-off and

storage is computed from the water balance at the soil surface

•P = F + ∆S + RO

Methodology

• Designate Test Area (Animal Science Watershed, Tippecanoe County).

• Obtain Data needed for analysis (referred to Rhea Sammon’s

thesis’ ABE 2002)

• Perform DRAINMOD Simulations

• Calibrate the model.

• Discuss the results and perform a sensitivity analysis based on the results

Results

Variation of drainage with Soil Types (Drummer and Toronto 1)

Variation of drainage and seepage with respect to the design parameters (Sensitivity Analysis)

Variation of drainage with Soil Types

• Hydraulic Conductivities:

Drummer: 0.17 cm/hrToronto 1: 0.153

cm/hr

Drainage Flow in Different Soil Types

0.00E+00

1.00E-01

2.00E-01

3.00E-01

4.00E-01

5.00E-01

6.00E-01

7.00E-01

8.00E-01

9.00E-01

1.00E+00

0 100 200 300 400

Julian Date

Drain

ag

e (cm

)

Modelled Drummer

Modelled Toronto

Variation of Drainage with Drain Depth for different Soil Types

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 20 40 60 80 100 120 140 160

Depth (cm)

Drummer

Toronto 1

Variation of Drainage w ith Drain Spacing for different Soil Types

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Spacing (cm)

Drummer

Toronto

Variation of Drainage with Initial Depth to Water table for different Soil Types

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 20 40 60 80 100 120

Depth (cm)

Drummer

Toronto 1

Variation of Drainage w ith Depth of Restricting Layer for different Soil Types

0

0.002

0.004

0.006

0.008

0.01

0.012

0 50 100 150 200

Depth (cm)

Drummer

Toronto 1

Sensitivity AnalysisVariables Values of Input

ParameterDrainage (cm)

(output)Sensitivity Seepage (cm)

(output)Sensitivity

Minp1

Maxp2

Minb1

Max b2

Minb1

Max b

2

Drain Depth 91.44 121 0 0.01 7.19 36.89 36.87 -0.02

121 152 0.01 0.02 2.94 36.87 36.86 -0.001

Drain Spacing 1500 2400 0.06 0.02 -2.17 36.82 36.85 0.002

2400 4163 0.02 0.01 -1.67 36.85 36.87 0.001

Effective Radius of Drain

1.9 2.54 0.01 0.01 0 36.87 36.87 0

2.54 3.3 0.01 0.01 0 36.87 36.87 0

Drainage Co-efficient 1 1.8 0.01 0.01 0 36.87 36.87 0

1.8 3.81 0.01 0.01 0 36.87 36.87 0

Initial Depth to Water Table

0 60 0.03 0.01 -0.5 39.6 36.87 -0.036

60 100 0.01 0 -3 36.87 33.6 -0.19

Depth to Restricting Layer

125 135 0 0.01 26 31.19 32.11 1

135 180 0.01 0.01 0 32.11 36.87 0.38

Thickness of the Restricting

layer

25 71 0 0.01 2.08 32 36.87 0.15

71 100 0.01 0.01 0 36.87 39.94 0.24

Vertical Hydraulic Conductivity of the restricting layer

0.035 0.085 0.04 0.02 -0.8 36.84 36.86 0.8

0.085 0.17 0.02 0.01 -1 36.86 36.87 1

Variation of Drainage with Spacing of Tile Drain

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 1000 2000 3000 4000 5000

Spacing (cm)

Dra

inag

e (c

m)

Drainage

Variation of Drainage w ith Depth of Tile Drain

0

0.002

0.004

0.006

0.008

0.01

0.012

0 50 100 150 200

Depth (cm)

Dra

inag

e (c

m)

Drainage

Variation of Drainage with Vertical Hydraulic Conductivity of the Restricting Layer

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 0.05 0.1 0.15 0.2

Hydraulic Conductivity (cm/hr)

Dra

inag

e (c

m)

Drainage

Variation of Drainage with Initial Depth of Water Table

0

0.005

0.01

0.015

0.02

0.025

0 50 100 150

Depth (cm)

Dra

inag

e (c

m)

Drainage

Variation of Seepage with Depth of the Restricting Layer

0

10

20

30

40

50

0 50 100 150 200

Depth (cm)

See

pag

e (c

m)

Seepage

Variation of Seepage with thickness of the Restricting Layer

0

10

20

30

40

50

60

70

0 50 100 150 200

Depth (cm)

See

pag

e (c

m)

Seepage

Variation of Seepage with Iniatial Depth of Water Table

35

36

37

38

39

40

41

0 50 100 150

Depth (cm)

See

pag

e (c

m)

Seepage

Variation of Seepage with Vertical Hydraulic Conductivity of the Restricting Layer

38.50538.51

38.51538.52

38.525

38.5338.535

38.5438.545

0 0.05 0.1 0.15 0.2

Hydraulic Conductivity (cm)

See

pag

e (c

m)

Seepage

Discussion• The drainage is highly sensitive to the

following parameters:

• Drain Depth• Drain Spacing

• Soil Types• Initial Depth to Water Table

• Hydraulic Conductivity of the Restricting Layer

• Thickness of the Restricting Layer• Depth to the Restricting layer

Discussion Cont……• Whereas Seepage is highly

sensitive to the following parameters:

• Initial Depth to Water Table

• Hydraulic Conductivity of the Restricting Layer

• Thickness of the Restricting Layer

• Depth to the Restricting layer

Conclusion The sub-surface drainage flow is highly sensitive to the Soil Type and

also on the depth, thickness and hydraulic conductivity of the restricting layer. Higher Hydraulic conductivity leads

to reduced drainage

Conclusion Cont……• Decrease in the depth of the

Restricting Layer increases drainage

• Increase in the thickness of the restricting layer increases drainage

• Decrease in the hydraulic conductivity of the restricting layer increases drainage

Thank You!